Light scattering in participating media is responsible for many natural phenomena. Simulating the evolution of volumetric media over time, as well as the complex light transport within it, are difficult problems in animation. Recent advances have made it feasible to incorporate a wider range of such effects in feature animation production; however, most of this work has focused on accelerating computation and increasing accuracy. Given physically accurate techniques, manipulating physical parameters to attain a target look is a challenging process. Previous work addresses this problem by investigating art-directable control of light transport for surface reflectance. However, artistic authoring and manipulation of volumetric lighting remains a largely unsolved problem.
While physically accurate and art-directable rendering have seemingly conflicting goals, recent efforts to incorporate physically-based rendering into production have shown great potential. Such techniques are seeing increased adoption because they provide complex and subtle lighting which would otherwise take extensive manual manipulation to replicate with ad-hoc techniques. Unfortunately, physically-accurate rendering is often not sufficiently expressive for the caricatured nature of animated films: though physically-based rendering may provide a great starting point, the challenge then becomes introducing controls necessary to obtain a desired artistic vision.